1. Field of the Invention
The present invention relates to a semiconductor laser, a method for manufacturing a semiconductor laser, an optical pickup, and an optical disk device, and particularly is suitable for being applied to a semiconductor laser based on a nitride III-V compound semiconductor, and an optical disk device and an optical pickup that include this semiconductor laser as the light source.
2. Description of the Related Art
To achieve self-pulsation (self-oscillation) operation in a semiconductor laser, a saturable absorber region needs to be provided inside the semiconductor laser. Ways for providing the saturable absorber region include a method in which the saturable absorber regions are formed in the partial portions of an active layer that are on both the sides of a ridge stripe and into which current is not injected at the time of the operation. In this method, the effective refractive index difference Δn between the partial portion in the active layer plane corresponding to the center part of the ridge stripe and the partial portions in the active layer plane on both the sides of the ridge stripe is set small to thereby form the saturable absorber regions (weakly index guide structure). To set the difference Δn small, the ridge stripe is so formed as to have small height (depth) so that the distance between the bottoms of the parts on both the sides of the ridge stripe and the upper surface of the active layer may be large. Semiconductor lasers that are based on a nitride III-V compound semiconductor and achieve self-pulsation operation by such a method have been proposed (refer to e.g. Japanese Patent Laid-open No. 2000-277859 and Japanese Patent Laid-open No. 2001-274514).